Bowling balls in recent years have been made from or surfaced with ebonite (rubber vulcanized with enough sulfur to make it quite hard) or from any of a variety of synthetic resins such as phenolic resins, epoxy resins, or polyester resins. Such balls are strong and durable but have a slick surface which causes them to slide for a considerable distance before undergoing true rolling, and are not easily induced to enter the "pocket" of the array of ten pins so as to cause a strike, in which all of the pins are tumbled.
It is known that better control, and better scores, can be obtained by altering either the surface of the bowling lanes, or of the balls, by application of temporary coatings, such as oil on the lanes, or softeners on the balls, or by making the balls with a surface containing gritty materials. Such expedients have either not appealed to the majority of bowlers or have been restricted by the rules of bowlers' organizations, such as hardness specifications for the surface of bowling balls.